The present invention relates to heat-curable silicone rubber compositions and particularly the present invention relates to heat-curable silicone rubber compositions which are hydrophilic and capable of dissipating static electricity.
Heat curable silicone rubber compositions are well known. Basically such compositions comprise a diorganopolysiloxane polymer, and extending or reinforcing filler, or mixtures thereof, which filler can be treated or untreated, and a peroxide curing catalyst. It is also common to facilitate the processing of such compositions by using various well known silicone process aids. The resulting ingredients are milled or mixed together in a doughmixer, formed to the desired shape and heated at elevated temperatures above 100.degree. C. to cure the composition to a silicone elastomer. Such compositions have well known properties as insulation for various purposes, such as for instance electrical insulation for electrical wire cables, etc. It has also become known in the technology to make such heat curable silicone rubber compositions conductive. Such conductive heat curable silicone rubber compositions are produced by incorporating to such composition conductive carbon black, or a metal or metal particles in the composition. The resulting heat curable silicone rubber composition which is conductive while suitable for many purposes has the disadvantage it does not act as an electrical insulation material and in addition, the presence of the carbon black makes it very hard in the cured form such that it has a Durometer of 50 and above.
Recently, in the industry it has become desirable to produce heat-curable silicone rubber compositions which are conductive enough to dissipate static electricity while at the same time the composition is soft that it has a Durometer in the neighborhood of 30. For instance, in hospital operating rooms, there is always the danger of an explosion due to the build-up of static electricity in various apparatus which may cause electrical charge to form a spark in the presence of potentially explosive gases or liquids.
Accordingly, for many applications in such hospital operating rooms, it is desired to utilize heat-curable silicone rubber compositions because of their inertness to various chemicals and agents. However, some heat-curable silicone rubber compositions had the disadvantage that they could build-up electrical charges which might cause a spark and result in a possible fire or explosion. Accordingly, to remove the possibility of such fires or explosions due to the accumulation of static electricity, conductive heat-curable silicone rubber compositions were formulated for various parts in the operating room. Such conductive heat-curable silicone rubber compositions being able to dissipate static electricity and thus removing the possibility of a fire or an explosion. However, such static dissipating conductive heat curable silicone rubber compositions as explained above had the disadvantage that they were hard and abrasive to the human skin.
Accordingly, it was highly desirable to have a heat-curable silicone rubber composition which was conductive enough to dissipate static electricity but still retained its inertness and insulative properties and also was soft. To produce such static dissipating heat-curable silicone rubber compositions, it was suggested by some that there be incorporated into heat-curable silicone rubber compositions as static electricity dissipating additives, glycerin and polyethylene oxide glycol compounds. While such materials did result in a heat-curable silicone rubber composition which was conductive enough to dissipate static electricity, it had several disadvantages. One of the disadvantages of such compositions is they tended to have low physical properties, that is a very low tear and a very low tensile strength. It was also found in some cases that the glycerine additive or the glycol polyether additives in some cases interfere with the peroxide cure of the composition to form a silicone elastomer. Accordingly, it was highly desirable to find substitutes for such glyverin and glycol polyethers which could be added to heat-curable silicone rubber compositions to make such heat-curable silicone rubber composition sufficiently conductive to dissipate static electricity while the compositions retain their physical properties and in which such heat-curable silicone rubber compositions still had the desired insulative properties and softness. Also it was desirable to find static electricity dissipating additives for heat-curable silicone rubber compositions which additives did not interfere with the cure of the composition.
It is also desirable in the health care area to produce elastomers which are hydrophilic. Specifically, heat-curable silicone rubber compositions because of their inertness have a good suitability for the fabrication of parts where an elastomer is necessary. However, such silicone elastomers produced from heat-curable silicone rubber compositions have the disadvantage that they are not hydrophilic. Accordingly, it is desirable that such silicone elastomers have hydrophilic surfaces so they may become compatible for the various uses that they may be put to in the health care area. Thus, it is desired the heat-curable elastomer be hydrophilic such that they are compatible with various parts of the physical anatomy. Accordingly, for instance it is highly desirable that heat-curable silicone elastomers be hydrophilic so that they are compatible with blood plasma. Various methods were tried to make such heat-curable silicone elastomers hydrophilic, such as treating the surfaces of such silicone elastomers with various chemicals and ingredients so as to make the surface of the silicone elastomer hydrophilic.
Accordingly, it is highly desirable to be able to incorporate a static dissipating ingredient which is non-toxic and compatible with standard heat-curable silicone rubber compositions so as to make such heat-curable silicone rubber compositions hydrophilic.
Further, in the copying art for various rollers utilized in copying machinery, it is desirable to have present rollers made of a material which is static dissipating but have good physical properties.
In addition, prior art static-dissipating heat-curable compositions tended not to bond very well to substrates even with the use of primers.
Accordingly, it is one object of the present invention to provide for a heat-curable silicone rubber composition which is capable of dissipating static electricity.
It is another object of the present invention to provide for a heat-curable silicone rubber composition which is capable of dissipating static electricity and is hydrophilic in nature.
It is still another object of the present invention, to provide for a hydrophilic, static electricity dissipating, heat-curable silicone rubber composition which is suitable for the health care area and which has good physical properties, that is cured elastomer is soft.
It is yet an additional object of the present invention to provide a process for producing a heat-curable silicone rubber composition which is capable of dissipating static electricity, is hydrophilic in nature and has good physical properties, as well as provides good bonds to substrates with the use of primer compositions. These and other objects of the present invention are accomplished by means of the invention set forth hereinbelow.